4. (a) Propene is a gaseous hydrocarbon - Edexcel - GCSE Chemistry - Question 4 - 2015 - Paper 1

According to the balanced equation:

$N₂(g) + 3H₂(g) ⇌ 2NH₃(g)$

We see that 1 mole of nitrogen reacts with 3 moles of hydrogen. Therefore, the volume of nitrogen needed can be calculated using the ratio:

$\frac{V(N_2)}{V(H_2)} = \frac{1}{3}$

For 1000 dm³ of hydrogen:

$V(N_2) = \frac{1000 \text{ dm³}}{3} = 333.33 \text{ dm³}$

Thus, you should put a cross in the box next to A (333 dm³).

At equilibrium, the reaction:

$N₂(g) + 3H₂(g) ⇌ 2NH₃(g)$

will have all three gases present: nitrogen (N₂), hydrogen (H₂), and ammonia (NH₃). This is because equilibrium does not favor one side completely; it establishes a balance between the forward and reverse reactions, which means leftover reactants (N₂ and H₂) and products (NH₃) will exist in the system.

Increasing the pressure generally shifts the equilibrium position to the side with fewer moles of gas, according to Le Chatelier's Principle. In this reaction:

• Reactants: 1 (N₂) + 3 (H₂) = 4 moles of gas
• Products: 2 moles of (NH₃)

Thus, more ammonia (NH₃) will be produced, increasing the yield under higher pressure conditions.

Higher pressure leads to gas molecules being closer together, thereby increasing their concentration. This results in:

• Increased frequency of collisions between reactant molecules.
• A higher reaction rate, consequently allowing the attainment of equilibrium faster than at lower pressures.